This invention relates to aqueous dispersions of plasticized polymer particles.
For the use of polymeric materials in certain applications, such as in coatings, it is often desirable to employ the polymer as a dispersion of small (i.e., 0.1 to 10 microns) particles in a continuous aqueous phase. While certain polymers are prepared directly as a dispersion using an emulsion polymerization process, it is often desirable to prepare the polymer by processes other than emulsion polymerization. Furthermore, many polymers are not amenable to an emulsion polymerization process. In such cases a dispersion must be prepared by dispersing a previously formed polymer into an aqueous phase. These so-called "artificial latexes" contain an emulsifying agent, i.e., a surfactant, which facilitates dispersion of the polymer and prevents the dispersed polymer particles from agglomerating, or settling out of the dispersion. Unfortunately, however, this surfactant generally remains with the polymer upon coalescence of the dispersed particles such as in film formation. This residual surfactant can phase out the coalesced polymer, or interact with water which comes into contact with the polymer, thereby impairing the properties of the polymer. In addition, this residual surfactant often imparts some hydrophilic character to the coalesced particles which is undesirable in certain applications, such as in electrostatic coatings, where good electrical resistance is desired.
Moreover, many polymers must be plasticized in order to impart to the polymers the physical characteristics necessary for their intended use. Such plasticization is generally effected by adding to the polymer a compound which improves the physical characteristics thereof. In conventional "artificial" latexes, such plasticizers are often added to the microdispersion after the polymer is dispersed into the aqueous phase. Thus, plasticization of conventional "artificial" latexes requires the insertion of an additional component and, often, an additional processing step into the preparation of the dispersion.
Accordingly, it would be desirable to provide a stable dispersion of a water-insoluble polymer which, when coalesced into the desired form, contains no surfactant which can phase out of the polymer. It would further be desirable to provide a dispersion of a water-insoluble polymer which does not require the addition of a plasticizer after the dispersion of the polymer into the aqueous phase.